Clear plastic ophthalmic lenses which provide good imaging qualities while reducing the transmission of incident light into the eye are needed for a variety of applications including use in sunglasses, fashion lens, prescription sport masks, face shields, and goggles. For these and other applications, ophthalmic lenses preferably are also scratch resistant.
Tinting is a common method for reducing the transmission of incident light through clear plastic materials, such as is used to form plastic ophthalmic lenses. Tinting refers to a process for treating a clear material to reduce the through transmission of light at particular wavelengths. The optical qualities introduced to a material by the tinting process are commonly characterized by the wavelengths of light transmitted and absorbed by the tinted material. The intensity of tinting, also commonly referred to as transmission loss, refers to the degree to which the tinted material reduces the intensity of light which passes through the tinted material. As much as a 60-90% reduction in light transmission can be achieved through tinting.
One common method for tinting involves dipping the material to be tinted into an aqueous solution of a dye at an elevated temperature, generally between about 85-95.degree. C. At these elevated temperatures, tinting is generally accomplished in about 3-60 minutes. Elevated temperatures are used to accelerate the absorption of the dye into the material being tinted. The tinting conditions used for a particular material depends on the physical qualities of the material to be tinted. For example, the maximum temperature at which tinting can be performed is limited by the temperature stability of the plastic material and dyes.
Two types of plastics which are commonly used to form ophthalmic lenses are poly(diethyleneglycol) bis allyl carbonate, tradenamed CR-39, and a bisphenol A based polycarbonate, commonly called PC. These plastics are generally tinted by dipping the plastics in an aqueous solution of a dye. Another type of plastic used to form ophthalmic lenses is polymethylmethacrylate, tradenamed PMMA. PMMA has a glass transition temperature which is too low for it to withstand the temperatures used in the dipping method of tinting. Instead, tinting of PMMA plastic is performed by other methods.
CR-39 plastic can be readily tinted since it is able to absorb dyes from an aqueous solution and is stable at elevated bath temperatures. One disadvantage associated with using tinted CR-39 is that it has inferior scratch resistance when dispensed uncoated. Although coatings are available which enhance the scratch resistance of plastic surfaces, these scratch resistant coatings are not generally applied to CR-39 because the coatings tend to reduce the tintability of the underlying substrate by blocking the ingress of dye.
Although PC plastic is stable at elevated tint bath temperatures, PC plastic does not readily absorb dyes from an aqueous bath. As a result, PC plastic is not usually tinted by introducing a dye into the plastic. Instead, PC plastic is more commonly tinted by coating the plastic with a material which can absorb dyes from an aqueous bath. Current coating products for PC plastic include a material which is applied to the PC plastic as a thin liquid coating and then cured to form a single film layer over the PC plastic surface.
The surface of uncoated PC plastic is too soft and too readily scratched to be dispensed without the use of a scratch resistant coating. Hence, in addition to a film layer for tinting PC plastic, a film layer is also needed which enhances the scratch resistance of PC plastic. This scratch resistant layer may be the same layer used to tint the PC plastic or may be separate from the layer used to tint the PC plastic.
It is generally difficult to render a material both highly tinted and highly scratch resistant. As the tintability of a coating increases, the scratch resistance of the coating usually decreases and vice versa. This is probably because coatings which have a relatively low cross-link density and a loose network structure facilitate the infusion and transport of dye into a material to tint the material. By contrast, coatings which have a relatively high cross-link density and a tight network structure generally exhibit greater scratch resistance.
A need exists for a coating or combination of coatings which render a material both highly tinted and highly scratch resistant. A need also exists for a method for rendering the material both highly tinted and highly scratch resistant. A need also exists for a method for forming ophthalmic lenses which are both highly tinted and highly scratch resistant. These and other objects are achieved by the present invention which is described herein.
The present invention relates to coatings and methods for tinting a plastic material such that the plastic material is rendered both highly tinted and highly scratch resistant. One embodiment of the invention relates to a dual layer coating for tinting a material and rendering the surface of the tinted material highly scratch resistant. In this embodiment, the dual coating includes a dye reservoir layer formed over a surface of the material to be tinted and a hard coating layer formed over the dye reservoir layer.
The dye reservoir layer includes between about fifteen and eighty percent by weight of a flexible acrylated oligomer or acrylated oligomer/acrylate monomer blend resin, and one to seventy percent by weight of a mono vinyl functional reactive diluent.
The hard coating layer formed over the dye reservoir layer includes between about twenty and one hundred percent by weight of acryloylated alkane polyols, the alkane polyols containing up to about forty eight carbon atoms and at least three O-acryloyl(polyalkylene oxide)! groups, each polyalkylene oxide chain including between about one and twenty alkylene oxide groups, and between about ten and seventy percent by weight of polyacryloylated alkane polyols, the alkane polyols containing up to about twenty four carbon atoms and at least about two O-acryloyl groups.
The dye reservoir layer may also include:
between about five and sixty percent by weight of polyacryloylated alkane polyols, the alkane polyols containing up to about twenty four carbon atoms and at least about two O-acryloyl groups; and/or between about fifteen and seventy five percent by weight of a polyacrylated urethane, the urethane having a molecular weight of less about 3500 and at least about two acrylate groups; and/or PA1 between about one tenth and fifteen percent by weight of a non-vinyl functional plasticizer; and/or PA1 one or more from the group consisting of surfactants, anti-oxidants, anti-yellowing agents and stabilizers. PA1 one or more from the group consisting of surfactants, anti-oxidants, anti-yellowing agents and stabilizers; and/or PA1 up to about fifteen percent by weight of an adhesion promoting acrylated oligomer or acrylated oligomer/acrylate monomer blend resin; and/or PA1 up to about sixty percent by weight of a mono vinyl functional reactive diluent. PA1 between about thirty and sixty five percent by weight of alkane polyols, the alkane polyols containing up to about forty eight carbon atoms and at least about three O-acryloyl(polyalkylene oxide)! groups and wherein the polyalkylene oxide chains include between about one and twenty alkylene oxide groups; PA1 between about thirty five and sixty percent by weight of polyacryloylated alkane polyols, the alkane polyols containing up to about twenty four carbon atoms and at least about two O-acryloyl groups; and PA1 between about two to ten percent by weight of an adhesion promoting acrylated oligomer or acrylated oligomer/acrylate monomer blend resin.
In one embodiment, the dye reservoir layer includes between about thirty five and sixty percent by weight of a flexible acrylated oligomer or acrylated oligomer/acrylate monomer blend resin, between about thirty and sixty percent by weight of a mono vinyl functional reactive diluent which includes O-acryloyl, and between about ten and thirty percent by weight of polyacryloylated alkane polyols, the alkane polyols containing up to about twenty four carbon atoms and at least about two O-acryloyl groups.
The hard coating layer may also include:
In one embodiment, the hard coating layer includes:
In one embodiment, the adhesion promoting resin is selected from the group consisting of acrylated urethane, acrylated epoxy and acrylated ester oligomer resins.
The present invention also relates to a tintable scratch resistant plastic. In one embodiment, the tintable scratch resistant plastic includes a clear plastic having a first surface, a dye reservoir layer formed over the first surface, and a hard coating layer formed over the dye reservoir layer. In another embodiment, the tintable, scratch resistant plastic includes a clear plastic having first and second surfaces. A dye reservoir layer is formed over the first surface, and a hard coating layer formed over the dye reservoir layer and over the second surface. In another embodiment, the tintable, scratch resistant plastic includes a clear plastic having first and second surfaces. A first and a second dye reservoir layer is formed over the first and second surfaces respectively. A first and second hard coating layer is formed over the first and second dye reservoir layers respectively.
The present invention also relates to a tinted scratch resistant plastic which includes a tintable scratch resistant plastic as described above in which the dye reservior layer further includes a dye.